The present invention relates to solid catalyst components using a novel carrier for use in the preparation of polyolefins and use thereof. More particularly, the present invention is concerned with solid catalyst components suitable for the preparation of polyolefins having superior particle properties such as, for example, high bulk density, large average particle diameter and reduced proportion of a fine powder, which catalyst components are capable of greatly increasing the polymer yield per solid and that per transition metal and hence permits the omission of the step for removing the residual catalyst from the polymer.
Heretofore, in this field of art there have been known various catalysts comprising an inorganic magnesium compound as carrier, e.g. magnesium halide or magnesium oxide, and titanium and/or vanadium supported thereon. However, polyolefins obtained by using such catalysts have a relatively small average particle diameter, a generally wide particle size distribution, a large proportion of a fine powder and a generally low bulk density.
Therefore, improvements have keenly been desired from the standpoint of productivity or polymer handling in the polymerization process. Further, also in molding those polymers, there arise problems such as the generation of dust and the deterioration of the molding efficiency. For this reason, it has been desired earnestly to increase the bulk density and decrease the proportion of a fine powder.
In an effort to solve the above-mentioned problems there also have been proposed many catalysts comprising a particulate carrier such as silica, alumina or silica-alumina and the foregoing magnesium compound and titanium and/or vanadium supported thereon (see, for example, JP1-11651B, JP1-12289B, JP60-149605A, JP62-32105A and JP62-207306A). Although polymers somewhat high in bulk density and large in average particle diameter can be obtained by using those known catalysts, a further improvement has been considered necessary for processing the polymer powder in a processing machine directly without going through a pelletizing step.
Using a catalyst comprising a zirconium compound (typically a metallocene compound) and an aluminoxane in the preparation of a polyolefin is known from JP58-19309A. The use of the said catalyst is advantageous in that ethylene copolymers can be produced in high yield. In many cases, however, such catalyst is soluble in the reaction system, so when used in slurry polymerization or vapor-phase polymerization, the resulting polymer is extremely low in bulk density and inferior in particle properties.
On the other hand, the use of a catalyst comprising a solid catalyst component and an aluminoxane, the solid catalyst component comprising a porous inorganic oxide carrier such as silica or silica-alumina and a transition metal compound supported thereon, has also been proposed, for example, in JP60-35006A, JP60-35007A and JP60-35008A. The use of a similar solid catalyst component including a porous inorganic oxide carrier has also been proposed, for example, in JP61-31404A, JP61-108610A and JP60-106808A. In many of the methods described in these prior art publications, however, by using such supported solid catalyst components, the polymerization activity is lowered to a large extent or particle properties of the resulting polymer are inferior, for example, the proportion of fine and coarse particles is large and the bulk density is low.
In JP63-234005A it is proposed to increase the molecular weight of the resulting polymer by using a transition metal compound having a 2-, 3- and 4-substituted cyclopentadienyl group, and for the same purpose, it is proposed in JP2-22307A to use a hafnium compound having a ligand combined with at least two crosslinked conjugated cycloalkadienyl.
As to these catalysts, however, their synthesis route and operations for their preparation are complicated, and in the case of using hafnium as a transition metal, the yield of the resulting polymer becomes lower. In many cases, moreover, these conventional catalysts are soluble in the reaction system, so their use in slurry polymerization or vapor-phase polymerization results in the formation of a polymer extremely low in bulk density and inferior in particle properties.
It is an object of the present invention to solve the above-mentioned problems of the prior art.
It is another object of the present invention to provide a catalyst component and a catalyst capable of greatly increasing the polymer yield per solid and that per transition metal to the extent of eliminating the need of removing residual catalyst from the resulting polymer and also capable of affording a polyolefin having good particle properties such as, for example, high bulk density, large average particle diameter and reduced proportion of a fine powder, as well as a process for preparing an olefin polymer having such excellent properties.
Further objects of the present invention will become apparent from the following description.